A number assignment module (NAM) is a memory storage in a mobile device which stores a telephone number and an electronic serial number. Phones with dual or multi NAM features offer users the option of registering the phone with more than one number. For example, this could be registering the phone with a local number in two separate markets.
Dual NAMs or alternative lines services have been available in code division multiple access (CDMA) and global systems for mobile communications (GSM) products for some time. For example, on CDMA products each NAM has its own mobile directory number (MDM), preferred roaming list (PRL), and other associate non-volatile memory items including the international mobile subscriber identity (IMSI) which makes the mobile device appear as a separate or a different subscriber to the network for billing purposes. This differentiation applies to voice services not to data services.
For data billing, data credentials such as the session initiation protocol (SIP) and a network layer protocol called mobile internet protocol (MIP) username and password are used. Further, an access node (AN) username/password for evolution-data optimized networks can be used.
Current implementations of non-volatile memory support only one number assignment module storage space for data credentials. Due to this limitation the mobile would have to use the first data credentials even though the user had switched to the second NAM (NAM2), thus causing the network to bill the NAM2 user for all voice services but still bill the first NAM (NAM1) subscriber for data services.
In addition, not all carriers and their customer's require the dual NAM features on their handset. For example, carrier A may not want this feature on any of their handsets, whereas carrier B may want the feature on some of their handsets where specific customers require the advanced feature. Further, a first customer on the second carrier may want to have to have dual NAM functionality with separate data billing for each NAM while a customer B on the second carrier may want all data billed to NAM1 only.